It is considered that industrial utilization forms of a femto base station (Home Node B; hereinafter abbreviated as HNB) include, for example, a form of utilization as a small wireless base station intended for home use, and a form of utilization as a small wireless base station in a corporation.
A case of providing service by the HNB includes, for example, the following advantages:
(1) Capability for providing a call service in a blind zone, where radio waves from a macro base station do not reach;
(2) Capability for providing a billing service less expensive than typical services provided by the macro base station;
(3) Capability for taking advantage of speed-enhancement technologies of 64QAM (64 Quadrature Amplitude Modulation) and MIMO (Multiple Input Multiple Output) and thereby allowing a high-speed packet service subordinate to the HNB to be provided, because the distance between a base station and a mobile station is short and the mobile station can attain high wireless quality (Ec/Io); and
(4) Capability for providing a specific content service taking advantage of locality of the HNB.
As described above, service by HNB includes a lot of advantages. Accordingly, it is preferable to provide the service only for subscribers having signed a contract with a carrier and subscribers that the owner of the HNB permits.
Thus, the 3GPP (3rd Generation Partnership Project), in release 8, has introduced a CSG (Closed Subscriber Group) such that only mobile stations in a permitted group can access the HNB and enjoy the service.
The CSG will herein be described in detail with reference to FIG. 1.
A third generation mobile communication system shown in FIG. 1 includes HNB 20, femto base station gateway (Home Node B GW; hereinafter abbreviated as HNB-GW) 30, circuit switching station (Mobile Switching Center; hereinafter abbreviated as MSC) 40, packet switching station (Serving GPRS Support Node; hereinafter abbreviated as SGSN) 50, and third generation mobile stations 10-1 and 10-2.
In FIG. 1, mobile station 10-1 among mobile stations 10-1 and 10-2 residing in an area subordinate to HNB 20 is an authorized mobile station. On the other hand, mobile station 10-2 is a mobile station that intends to receive a service by HNB 20 in an unauthorized manner, and hereinafter is referred to as unauthorized mobile station 10-2. In the case of a mobile station that does not identify itself, such a mobile station will be referred to as mobile station 10.
HNB 20 is connected to a core network of an operator via HNB-GW 30.
The core network, which is a core network apparatus, includes MSC 40 that controls circuit switching and SGSN 50 that controls packet switching.
If HNB 20 supports a CSG function, HNB 20 notifies mobile station 10 residing in an area subordinate to HNB 20 of the CSG identifier (CSG identity) of the own CSG cell.
Mobile station 10-1 decodes the CSG identifier notified from HNB 20, and determines whether the CSG identifier is included in a CSG list included in mobile station 10-1.
If the CSG identifier is included in the CSG list, mobile station 10-1 camps on a CSG cell where mobile station 10-1 resides, and is capable of enjoying various services, such as origination of a call and reception of an incoming call.
On the other hand, if the CSG identifier is not included in the CSG list, mobile station 10-1 does not camp on the CSG cell where mobile station 10-1 resides, but performs an operation of selecting an appropriate CSG cell other than the CSG cell concerned.
This mechanism enables only selected mobile station 10-1 with CSG identifier of the CSG cell of HNB 20 to access HNB 20.
However, a case can be supposed where it is intended to receive a service in an unauthorized manner in an originally inaccessible CSG cell of HNB 20 as with unauthorized mobile station 10-2 shown in FIG. 1 even though the CSG function is supported.
In such a case, MSC 40 or SGSN 50 checks the IMSI (International Mobile Subscriber Identity) of mobile station 10 and the CSG identifier of the CSG cell where mobile station 10 resides, and thereby performs access regulation that regulates access from mobile station 10 to HNB 20 (3GPP TS25.467 Ver 8.0.0 Section 5.1.3).
On the other hand, because the CSG function has been introduced from release 8 of 3GPP, there was a case where mobile station 10-1, before release 8, did not support the CSG function. Further, there is a case where HNB 20 does not support the CSG function.
In these cases, HNB 20 performs an identification procedure (3GPP TS24.008 Ver 8.4.0) on mobile station 10-1 in order to inquire about the IMSI of mobile station 10-1. HNB 20 performs an HNBAP (HNB Application Part): UE REGISTER REQUEST procedure (3GPP TS25.469 Ver 8.0.0) on HNB-GW 30 in order to register mobile station 10-1 in HNB-GW 30. Here, HNB-GW 30 checks whether the IMSI of mobile station 10-1 is accessible or not to HNB 20, and thereby regulates access.
When HNB-GW 30 determines that mobile station 10-1 is accessible to HNB 20, HNB-GW 30 notifies HNB 20 that access is permitted, by means of an HNBAP: UE REGISTER ACCEPT message. Accordingly, the service by HNB 20 is provided for mobile station 10-1.
On the other hand, if mobile station 10 is unauthorized mobile station 10-2 shown in FIG. 1, the IMSI of unauthorized mobile station 10-2 will not have been registered to be accessible to the CSG. Accordingly, HNB-GW 30 determines that unauthorized mobile station 10-2 cannot access HNB 20, and notifies HNB 20 that access cannot be permitted, by means of HNBAP: UE REGISTER REJECT message. This terminates an RRC (Radio Resource Control) connection between unauthorized mobile station 10-2 and HNB 20 (3GPP TS25.467 Ver 8.0.0 Section 5.1.2).
As described above, in a case of providing the service by HNB 20, if unauthorized mobile station 10-2 whose access to HNB 20 is not permitted originates a call, the mobile communication network rejects access to HNB 20 in a signal establishment process because MSC 40, SGSN 50 or HNB-GW 30 regulates access on the basis of the IMSI of mobile station 10.
On the other hand, 3GPP standardization specifies that even mobile station 10 originally inaccessible to HNB 20 can originate a call if the call type is an emergency call (3GPP TS22.011 Ver 8.6.0 Section 8.5.1).
If the call type is an emergency call, mobile station 10-1 sets “Emergency Call” to an Establishment Cause parameter representing the cause of an establishment request in RRC: RRC CONNECTION REQUEST message or RRC: INITIAL DIRECT TRANSFER to be transmitted to HNB 20 on a RRC connection establishment request or a signaling connection establishment request (3GPP TS25.331 Ver 8.5.0 Section 10.3.3.11, Patent Literature 1).
HNB 20 then sets an “Emergency Call” value to a Registration Cause parameter in a HNBAP: UE REGISTER REQUEST message to be transmitted to HNB-GW 30.
If the Registration Cause parameter is “Emergency Call”, HNB-GW 30 does not perform access regulation based on the IMSI (3GPP TS25.467 Ver 8.0.0 Section 5.1.2).
This method enables even mobile station 10 that originally is unable to access to HNB 20 to skip the access regulation of HNB-GW 30 and to access HNB 20 if the call type is an emergency call.
Here, FIG. 2 shows a configuration of an RRC: RRC CONNECTION REQUEST message; FIG. 3 shows a configuration of an RRC: INITIAL DIRECT TRANSFER message; FIG. 4 shows a configuration of the Establishment Cause parameter of an RRC protocol; FIG. 5 shows a configuration of an HNBAP: UE REGISTER REQUEST message; and FIG. 6 shows a configuration of a Registration Cause parameter of an HBNAP protocol.